– The backup saves your settings and usage history (for all your SIM cards). It does not save the widgets, you’ll have to recreate them after a restore.
– It is recommended to restore from backups made the same day. While it’s technically possible to restore older backups, it raises a number of potential issues and the need to merge some data may yield surprising results. Additionally it is not always possible to restore a backup done prior to an update as the format of the backup file may have changed in the new version.
– An hourly auto-backup is available, you can enable it in Settings > Misc > Auto backup. Only the two latest backups are kept on the SD card.